As fibers or filaments having high strength and high heat resistance, there are known polybenzazole fibers or filaments comprising polybenzoxazole or polybenzothiazole, or a copolymer thereof.
Generally, polybenzazole fibers or filaments are produced by extruding from the spinneret a dope containing the above polymer or copolymer and an acid solvent; dipping the fibers or filaments of the dope in a fluid such as water or a mixture of water and an inorganic acid, thereby solidifying the same; thoroughly washing the fibers or filaments in a water bath to remove most of the solvent; allowing the fibers or filaments to pass through a bath holding an aqueous solution of an inorganic base such as sodium hydroxide or the like to thereby neutralize the residual acid which is not extracted from the fibers or filaments; and drying the same.
The polybenzazole fibers or filaments thus produced have found a variety of applications, because they are superior in mechanical properties such as strength, and also higher in heat resistance, as mentioned above. Recently, the polybenzazole fibers or filaments are demanded to have further improved properties, particularly to sufficiently maintain the strength even after exposed to atmospheres of high temperatures and high humidity over long periods of time.
The polybezazole fibers or filaments are used as heat resistant cushion materials for supporting hot products without flawing them, in the manufacturing steps in the fields of iron and steel, ceramics and non-ferrous metal industries, because of their superior mechanical properties such as high strength and high heat resistance. When the polybenzazole fibers or filaments are used as heat resistant cushion materials, they are used for hot products which mostly maintain temperatures of 350° C. or higher immediately after subjected to molding. In some cases, the heat-accumulated cushion materials (or felt materials) are used while being cooled with water. Therefore, recently, there are earnest demands for felt materials comprising the polybenzazole fibers or filaments which can sufficiently maintain the strength even when exposed to atmospheres of high temperatures and high humidity over long periods of time.
Further, the polybenzazole fibers or filaments are used as textile materials for protective materials, proof clothing and industrial materials, because of their superior mechanical properties such as strength and elastic modulus. However, the polybenzazole fibers or filaments are expected to have further improved properties. Particularly, there are demands for woven or knit fabrics made from polybenzazole fibers or filaments capable of sufficiently maintaining the strength when exposed to atmospheres of high temperatures and high humidity and light irradiation over long periods of time.
While nylon fibers, polyester fibers, glass fibers and steel fibers are mainly used as rubber reinforcements for tires, hoses, belts, etc., recently, aromatic polyamide fibers, represented by Kevlar, having high strength and high elastic modulus are used as rubber reinforcements. On the other hand, the polybenzazole fibers or filaments have attracted the attentions of those skilled in the art as rubber reinforcements, since they have far higher strength and elastic modulus and superior heat resistance and dimensional stability as compared with the aromatic polyamide fibers. The use of the polybenzazole fibers or filaments as reinforcing fibers in the applications required to have higher strength and higher heat resistance is contemplated in the field of rubber materials for which the existing organic fibers are insufficient as reinforcing fibers in view of mechanical properties. As mentioned above, the polybenzazole fibers or filaments are used as the rubber-reinforcing fibers, because of the excellent mechanical properties such as strength and elastic modulus. Especially, there are earnest demands for rubber reinforcement comprising such polybenzazole fibers or filaments that can sufficiently maintain the strength when dynamic fatigue is applied to a reinforced rubber body containing the same and when the rubber body has a high temperature and high humidity therein.
Steel has hitherto been used as a reinforcement for cement/concrete, and recently, reinforcements containing glass fibers, carbon fibers or aramid fibers have been developed and put into practical use. Carbon fibers are very excellent in mechanical properties but are electrically conductive, and therefore can not be used in the proximity of power lines. On the other hand, aramid fibers have relatively sufficient properties, but have lower elastic modulus than carbon fibers, and therefore, their reinforcing effects are poor. Cement/concrete-reinforcing sheets comprising the polybenzazole fibers or filaments exhibit higher reinforcing effects over the aramid fibers and carbon fibers, and thus are expected as products of the next generation. The polybenzazole fibers or filaments are used in the cement/concrete-reinforcing sheets, because of their excellent mechanical properties such as strength and elastic modulus as mentioned above, but are demanded to be further improved in light resistance and the like. Especially, there are earnest demands for polybenzazole fiber sheets for reinforcing cement/concrete, capable of sufficiently maintaining the strength when exposed to atmospheres of high temperatures and high humidity over long periods of time.
Reinforcing steels have hitherto been used as rod-like cement/concrete reinforcing materials, and recently, reinforcing materials comprising aramid fibers have been developed and put into practical use. The marked features of aramid fiber rods rest in non-magnetism and non-electric conductivity, and thus, they can be used as the reinforcing rods of cement/concrete constructions in which the reinforcing steels can not be used. Polybenzazole fiber rods which are likewise non-magnetic and non-conductive show superior reinforcing effects over the aramid fiber rods and are expected as products of the next generation. The polybenzazole fibers or filaments, excellent in mechanical properties such as strength and elastic modulus, are used as reinforcing materials for cement/concrete, but are demanded to be further improved in properties to thereby provide polybenzazole fiber rods for reinforcing cement/concrete, capable of sufficiently maintaining the strength when exposed to atmospheres of high temperatures and high humidity over long periods of time.
The polybenzazole fibers or filaments excellent in mechanical properties such as strength and elastic modulus are used as textile materials for protective materials, proof clothes and industrial materials, as mentioned above. They are expected to have further improved properties. Especially, there are earnest demands for spun yarns comprising polybenzazole fibers or filaments capable of sufficiently maintaining the strength when exposed to atmospheres of high temperatures and high humidity and light irradiation over long periods of time.
As compounding materials for reinforcing fibers, glass fibers have been used. Recently, carbon fibers or aramid fibers are used to provide composite materials having higher strength and lighter weights, and such products have already been developed and put into practical use. Carbon fibers are very excellent in mechanical properties but are fragile because of the poor impact resistance. Aramid fibers are relatively sufficient in impact resistance, but are lower in elastic modulus than carbon fibers, and therefore show poor reinforcing effects. Composite materials comprising the polybenzazole fibers or filaments are sufficient in both impact resistance and elastic modulus, and show superior reinforcing effects over the composite materials comprising carbon fibers. Thus, the polybenzazole fiber composite materials are expected as products of the next generation.
The polybenzazole fibers or filaments are also used as the fiber-reinforced composite materials, because of their excellent mechanical properties such as strength and elastic modulus, as mentioned above, but are demanded to be further improved in properties such as light resistance and so on. Especially, there are earnest demands for composite materials comprising polybenzazole fibers or filaments excellent in durability and capable of sufficiently maintaining the strength when exposed to atmospheres of high temperatures and high humidity over long periods of time.
Sail cloths comprising the polybenzazole fibers or filaments are widely used. Especially, the sails of yachts for use in yacht races are required to have high resistance to pull strength and high tensile strength so that the sails of designed shapes can not be deformed by winds. Recently, lamination-molded sail cloths are dominantly used, which are manufactured by sandwiching a woven fabric or a scrim comprising fibers with high strength and high elastic modulus between two films such as polyester films and laminating them, and molding the lamination, as disclosed in U.S. patent Ser. Nos. 5,001,003 and 5,403,641. Further as disclosed in U.S. patent Ser. No. 5,097,784, a method of integrally molding a three-dimensional yacht sail is developed. Examples of the sail cloth referred to in the description of the present invention include such three-dimensional integrally molded articles. Paraaramid fibers and carbon fibers have been used for products made by such techniques. Carbon fibers have higher tensile modulus of elasticity than paraaramid fibers, and thus are expected to improve the performance of the sails of yachts, but such sails are weak against bending and thus poor in fatigue life. To overcome these problems, the sails of yachts comprising the polybenzazole fibers or filaments have been developed and have already proved their excellent performance in the world-wide yacht races. However, the yacht sails comprising the polybenzazole fibers or filaments have problems in that their initial performance is very high, but deteriorates due to solar light. Therefore, such yacht sails are broken, for example, in the course of a long term round-the-world yacht race. In such a long term race, a plurality of yacht sails are loaded on the yacht and are exposed to an atmosphere of high temperature and high humidity. The polybenzazole fibers or filaments tend to lower in strength under such an atmosphere, and therefore are demanded to have improved durability in this sense.
The polybenzazole fibers or filaments have been widely used for ropes such as yacht ropes which are required to have high strength and high abrasion resistance, because of their excellent mechanical properties such as strength and high heat resistance as mentioned above. However, the polybenzazole fibers or filaments are subject to mechanical damages in the course of the manufacturing of ropes, because of the very highly oriented molecular chain structures thereof. Therefore, the ropes comprising the polybenzazole fibers or filaments are inferior in long age durability under atmospheres of high temperatures and high humidity, as compared with the polybenzazole fibers or filaments themselves.
Aramid fibers have been used for knife proof vests so far. Lately, knife proof vests made from high strength polyethylene fibers have been developed and put into practical use. However, numerous aramid fibers are needed for such knife proof vests so as to exhibit required protective performance. Therefore, one can not continuously wear such a vest, because it is thick and heavy in weight and is not comfortable to wear. On the other hand, knife proof vests made from high strength polyethylene fibers are reduced in weight but not in thickness because the specific gravity thereof is small. Knife proof vests made from the polybenzazole fibers or filaments show superior protective performance to the knife proof vests of the aramid fibers and the knife proof vests of the high strength polyethylene fibers, and are expected as lightweight and thin knife proof vests of the next generation. While the polybenzazole fibers or filaments are used in knife proof vests because of their excellent mechanical properties such as strength and elastic modulus as mentioned above, further improvement of other properties such as light resistance are expected for the polybenzazole fibers or filaments. Especially, there are earnest demands for knife proof vests made from polybenzazole fibers or filaments capable of sufficiently maintaining the strength when exposed to atmospheres of high temperatures and high humidity over long periods of time.
While aramid fibers have hitherto been used for bullet proof vests, lately, bullet proof vests made from high strength polyethylene fibers have bee developed and put into practical use. However, numerous aramid fibers are needed for such bullet proof vests so as to exhibit required protective performance. Therefore, one can not continuously wear such a vest, because it is thick and heavy in weight and is not comfortable to wear. On the other hand, bullet proof vests made from high strength polyethylene fibers are reduced in weight but not in thickness because the specific gravity thereof is small. Bullet proof vests made from the polybenzazole fibers or filaments show superior protective performance to the bullet proof vests of the aramid fibers and the bullet proof vests of the high strength polyethylene fibers, and are expected as lightweight and thin bullet proof vests of the next generation. While the polybenzazole fibers or filaments are used in bullet proof vests because of their excellent mechanical properties such as strength and elastic modulus as mentioned above, further improvement of other properties such as light resistance are expected for the polybenzazole fibers or filaments. Especially, there are earnest demands for bullet proof vests made from polybenzazole fibers or filaments capable of sufficiently maintaining the strength when exposed to atmospheres of high temperatures and high humidity over long periods of time.
Under the foregoing circumstances, the present invention has been developed, and objects of the invention are to provide polybenzazole fibers or filaments whose strength hardly deteriorates even when exposed to atmospheres of high temperatures and high humidity over long periods of time, and the uses thereof.